To minimize the undesirable emissions at both low and high power operations of gas turbine power plants, it has been desirable to maintain control of equivalence ratio of the combustion process throughout the entire range of operation of the burner. When fuel is conventionally injected by the single nozzle constructions and this equivalence ratio is optimized at about unity for minimum emissions of carbon monoxide and unburned hydrocarbons at low powers, it may at high powers become as high as from 1.5 to 2.0. This situation leads to high emissions of both NOx and smoke at high powers.
Although alternative fuel nozzle arrangements have been used, the constructions generally have been directed toward improving the mixing close to the nozzle to obtain a high degree of fuel-air blending close to the nozzle in the hope of promoting cleaner and more complete combustion. These approaches lead to more complex combustors and fuel systems without significant reduction in the objectionable emissions. Multiple stage combustors such as that described in U.S. Pat. No. 3,872,664 have been proposed, in which combustion occurs in two or more discrete zones, in an attempt to achieve optimum equivalence ratio over the entire operating range. However, these concepts generally lead to the use of a multiplicity of fuel injector systems located in different positions.